ADS simulation problem: MOS transistor characteristic sim?

Dear all,

I wanted to use ADS to simulate some MOS transistor characteristic. I have successfully simulated and plotted the Drain current Vs Vds (in different Vgs). However, how could I plotted the graph of gm Vs Vgs in a fixed Vds?

Could anyone teach me?

thanks

use diff(Ids.i). It is a derivative of Ids with respected to Vgs.